1. Field of the Invention
The present invention relates to a ratchet-type lever mechanism for seat lifter (or seat height adjuster), which is operable by rotation of an operation lever to actuate the seat lifter for the height adjustment of seat. Particularly, the invention is directed to a ratchet-type lever mechanism having a ratchet gear system
2. Description of Prior Art
A seat height adjuster or what is known as a seat lifter is incorporated in automotive seat to enable an occupant on the seat to selectively adjust the height of seat according to his or her physique and seating posture. In the seat lifter, typically known is a linkage-type seat lifter having forward and rearward links which are interlockingly movable and pivotally coupled with the forward and rearward portions of the seat, respectively, so that the seat may be raised and lowered via those two links. This seat lifter includes plural transmission gears (reduction gears and the like), a brake unit, and a drive mechanism provided with a lever or handle, wherein the drive mechanism is operatively connected through the transmission gears and brake unit to the forward and rearward links. As known in the art, the brake unit provides a braking action on the drive mechanism to normally lock the links to a given position. Conventionally, a ratchet-type lever drive mechanism is disclosed in the Japanese Laid-Open Patent Publication No. 2000-255295, for instance. According thereto, an operating lever is connected with two ratchet pawl gears, and two ratchet wheel gears are fixed to the output shaft of the brake unit, such that, by vertical rotation of the operating lever, one of the two pawl gears may be selectively meshed with a corresponding one of the two ratchet wheel gears, thereby causing upward and downward motions of the seat lifter to raise and lower a seat to a desired level. The ratchet-type lever mechanism includes a pair of first and second ratchet wheel gears fixed to the shaft of brake unit, and a ratchet gear member having a pair of first and second toothed ratchet pawls extend continuously from the circumferential side thereof in an offset fashion with respect thereto, such that those two toothed ratchet are distant from each other by a certain central angle with respect to the central axis of ratchet gear member. The first ratchet wheel gear has a known one-way clutch built therein, by which the gear itself is only permitted to rotate together with the shaft of brake unit in clockwise direction to cause upward motion of the seat lifer, while being free to rotate about the brake unit shaft in anticlockwise direction. On the other hand, the second ratchet wheel gear has another one-way clutch therein for only permitting the gear itself together with the brake unit shaft to rotate in anticlockwise direction to cause downward motion of the seat lifter, while being free to rotate about the brake unit shaft in clockwise direction. Accordingly, with this conventional mechanism, upward rotation of the operation lever brings the first toothed ratchet pawl to meshed engagement with the first ratchet wheel gear, thereby causing upward motion of seat lifer to raise a seat. Conversely, downward rotation of the lever brings the second toothed ratchet pawl to meshed engagement with the second ratchet wheel gear, thereby causing downward motion of seat lifter to lower the seat.
In this prior art, the ratchet gear member is formed by casting into an integral one configuration including the first and second toothed ratchet pawls which are integral with the body of the ratchet gear member. Specifically, in the casting process, separate base materials for casting, such as a rotary shaft base material and two ratchet pawl base materials, are placed in casting dies and subjected to molding together therein, thereby producing one integral piece of ratchet gear member with two toothed ratchet pawls. However, this has been found defective because it involves complicated steps and increased costs, and also because the casting often creates different sizes of each resulting cast part, which will result in decreased productivity and increased costs. Further, in this sort of lever mechanism, a relatively long splined connection shaft is required for sufficient spline connection of the operating lever with such relatively thick cast ratchet gear member. But, in most cases, such lever mechanism has to be provided on the lateral wall of seat cushion and a quite small spacing is given between that seat cushion lateral wall and a door of vehicle. Consequently, there is a need to reform a local part of the seat cushion lateral wall to avoid undesired contact of the lever mechanism with the door, which also results in a poor productivity and increased costs.
In view of the above-stated drawbacks, it is a purpose of the present invention to provide an improved ratchet lever mechanism which is simplified in structure and is thin in thickness, thus allowing the mechanism per se to be installed in a narrow space between the lateral side of vehicle seat and a door of vehicle.
In order to achieve such purpose, a ratchet lever mechanism in accordance with the present invention is basically comprised of:
an output shaft element rotatably provided in the ratchet-type lever mechanism;
a ratchet gear wheel means rotatably provided in the ratchet-type lever mechanism, which includes a first ratchet gear wheel and a second ratchet gear wheel, wherein each of the first and second ratchet gear wheels has one-way clutch means built therein, with such an arrangement that the first ratchet gear wheel is to be locked to the output shaft element in a normal direction for rotation therewith, while being allowed to rotate in a reverse direction, and that the second ratchet gear wheel is to be locked to the shaft element in said reverse direction, while being allowed to rotate in the normal direction;
an input shaft element rotatably supported in the ratchet-type lever mechanism;
a ratchet pawl element so formed from a plate material to have: a flat body portion; a first toothed pawl portion; and a second toothed pawl portion, wherein the first and second toothed pawl portions extend from the flat body portion in a spaced-apart manner, such that the second toothed pawl portion is bent from the first toothed pawl portion in an offset relation with respect to the body portion;
the first and second toothed ratchet pawl portions being disposed in correspondence with the respective first and second ratchet gear wheels; and
a connecting means for connecting the ratchet pawl member to the input shaft element, which connecting means is defined in the input shaft element and the ratchet pawl member.
In one aspect of the present invention, the connecting means may comprise an uneven portion defined in the input shaft element; and an unevenly shaped hole formed in the ratchet pawl member. The ratchet pawl member may be connected to the input shaft element by engaging the unevenly shaped hole of ratchet pawl member about the uneven portion of input shaft element.
In another aspect of the invention, an operating lever is firmly attached to the input shaft element, and the connecting means may include a two-point connecting means for not only connecting the operating lever to the input shaft element at one point, but also connecting the operating lever to the ratchet pawl member at another point.
Other various structural features and advantages will become apparent from reading of the descriptions hereinafter, with reference to the annexed drawings.